Conventional anthraquinone blue dyes such as C. I. Disp. Blue 56 have been used to dye polyesters for a long time. However, they have several deficiencies such as: low hue intensity which incurrs extra costs for the dyeing process; tendency to easily contaminate other fibers than those to be dyed; likelihood of uneven dyeing; and, particularly, they are complexed with a metalic ion to form a metalic salt.
DE 3,821,338 Al discloses an improved blue dye composition which comprises the compounds of formulae (A), (B), (C) and (D): ##STR3## wherein R', R", R"' and R"" respectively represent an alkyl, arylalkyl, alkoxyalkyl, hydroxyalkyl, chloroalkyl or alkenyl group;
X represents Cl or Br; PA1 Y represents a cyano or nitro group; PA1 Y.sub.1 represents an alkyl, arylalkyl or alkoxyalkyl group; and PA1 Q represents an alkyl, aryl or alkoxy group.
The dye composition disclosed in the above German patent application, while successful in improving some of the above-mentioned disadvantages, still possesses various defects. For instance, release of the dye may occur during a continuous, high temperature dyeing process; the degree of exhaustion tends to be low; discoloration may occur during the permanent setting and ironing process of polyesters; and wash fastness is also poor. Further, in the process of dyeing a polyester and cotton fiber blend, the contamination is relatively high, and, therefore, the inherent color does not appear sufficiently after the completion of dyeing the blend, which may require another step of reducing/cleaning process employing a strongly toxic material.
In addition, the dye composition of the above-mentioned German patent application comprises a component having an alkoxy group (which is hydrophilic); accordingly, affinity of the dye with polyester (which is hydrophobic) is low, resulting in a substantial loss of the dye.